Disable tells PBP to STOP auto-insertion of interrupt checking code. Placing
disable "before" the interrupt service label doesn't actually disable interrupts.
It just tells PBP to stop automatically placing interrupt checking code between
each BASIC command. Your interrupt will work either way.

ON INTERRUPT GOTO ? tells PBP where the interrupt service routine is located.

Resume inserts RETFIE right at the end of your interrupt handler "code", and
that's where you want RETFIE to be.

Enable tells PBP to start auto-inserting interrupt testing code after each
BASIC instruction, and you want this at the very end or after RESUME. Just
like the ON INTERRUPT example shown in the manual.